1. Field of the Invention
This invention relates to processes for the preparation of polyurethane foams.
2. Description of the Prior Art
Triethylenediamine (i.e. 1,4-diazabicyclo[2.2.2]octane is currently the tertiary amine gelation catalyst of choice in the commercial production of polyurethane foams from diisocyanates and polyols. Triethylenediamine is generally recognized throughout the urethane industry as a superior gelation catalyst. It is normally employed for urethane foam formulations as a 33 weight percent solution in dipropylene glycol. Prior to the present invention, two alternative urethane foam gelation catalysts were N,N,N',N'-tetramethyl-1,2-ethanediamine (TMEDA) and N,N,N',N'-tetramethyl-1,3-butanediamine (TMBDA). However, said alternatives to the triethylenediamine gelation catalysts have never received widespread acceptance in the industry because (1) they are not as active and (2) they impart an objectionable odor to the foams produced with them.
The present invention is founded on the unexpected discovery that N,N,N',N'-tetramethyl-.alpha.,.omega.-polymethylenediamines wherein the methylene chain consists of from 4-8 methylene moieties are approximately as effective gelation catalysts as a 33 weight percent solution of triethylenediamine in dipropylene glycol. Moreover, at least some of the catalysts of the present invention (e.g. N,N,N',N'-tetramethyl-1,6-hexanediamine) lack the degree of objectionable odor characteristics of the known tetramethylediamine catalysts TMEDA and TMBDA.
Several references, e.g. Chem. Abstracts: 70:69085u (Kato), 71: 39830m (Strassel et al.), 75: 118837e (Neet et al.), and 81: 121781m (Gemeinhardt et al.), refer to "tetramethylbutanediamine" or "tetramethylbutylenediamine" as catalysts in urethane production. However, investigation of these references revealed that the specific compound referred to is the N,N,N',N'-tetramethyl-1,3-butanediamine mentioned above, a commercially available catalyst (TMBDA): they did not disclose the use of the N,N,N',N'-tetramethyl-1,4-butanediamine which is claimed in this invention.
Two references which do refer to the use of amines of this invention as catalysts for an isocyanate reaction are: de Aquirre et al., Chem. Abstracts, 63:9768a (1965) and Seki et al., Chem. Abstracts, 85:193596k (1976). However, neither one of them demonstrates the use of the N,N,N',N'-tetramethyl-.alpha.,.omega.-polymethylenediamines of this invention, i.e. (CH.sub.3).sub.2 NCH.sub.2 CH.sub.2 (CH.sub.2).sub.n CH.sub.2 CH.sub.2 N(CH.sub.3).sub.2 wherein n is 0-4, in the preparation of urethane foams, or in the catalysis either of the alcohol-isocyanate or the water-isocyanate reactions which predominate in that process (see below, in the EXAMPLES). The de Aquirre et al. abstract relates to a general kinetic study conducted in dilute solution on the reaction of phenyl isocyanate with amines or ureas as catalyzed by a variety of tertiary amines including N,N,N',N'-tetramethyl-1,6-hexanediamine. The Seki et al. abstract describes the use of both N,N,N',N'-tetramethyl-1,6-hexanediamine and N,N,N',N'-tetramethyl-1,4-butanediamine as cocatalysts with dibutyltin dilaurate or stannous octoate for the preparation of epoxypolyisocyanate (referring, it is believed, to polyisocyanurate) foams.
Finally, British Pat. No. 1,403,569 contains a general allusion to the use of tertiary amines as catalysts for the reaction of polyisocyanates with polyalcohols to form polyurethanes. Among the tertiary amines contemplated by the British patent is N,N,N',N'-tetramethyl-1,6-hexanediamine. The British patent contains no disclosure relating to any foam preparation, much less any disclosure of the unexpected beneficial results which can be obtained according to the present invention.